1. Field of the Invention
The present invention relates to the manufacture of aircraft, space vehicles and the like wherein panels are connected using friction stir welding. More particularly, the present invention relates to the construction of aircraft, space vehicles and the like wherein an improved method enables stringer stiffened panels to be joined with friction stir lap welds, in replacement of the traditional riveting practice.
2. General Background of the Invention
Friction stir welding (FSW) is a solid state joining process developed by The Welding Institute (TWI), Cambridge, England and described in U.S. Pat. No. 5,460,317, incorporated herein by reference. Compared with traditional fusion welding processes, it offers simplified processing, improved mechanical properties, diminished weld defect formation, equivalent corrosion resistance, and reduced distortion, shrinkage, and residual stresses. Using conventional milling equipment with a backside anvil support, a non-consumable, cylindrical pin tool is rotated and plunged into the butt or lap joint of the material to be welded. Pin tools are specifically designed for a given alloy and gauge. Also incorporated herein by reference are U.S. Pat. No. 5,718,366 and all references disclosed therein. The following additional references of possible interest are incorporated herein by reference: U.S. Pat. Nos. 3,853,258, 3,495,321, 3,234,643, 4,087,038, 3,973,715, 3,848,389; British Patent Specification No. 575,556; SU Patent No. 660,801; and German Patent No. 447,084. Publications that discuss friction stir welding include “New Process to Cut Underwater Repair Costs”, TWI Connect, No. 29, January 1992; “Innovator's Notebook”, Eureka Transfer Technology, October 1991, p. 13; “Repairing Welds With Friction-Bonded Plugs”, NASA Tech. Briefs, September 1996, p. 95; “Repairing Welds With Friction-Bonded Plugs”, Technical Support Package, NASA Tech. Briefs, MFS-30102; “2195 Aluminum-Copper-Lithium Friction Plug Welding Development”, AeroMat '97 Abstract; “Welding, Brazing and Soldering”, Friction welding section: “Joint Design”, “Conical Joints”, Metals Handbook: Ninth Edition, Vol. 6, p. 726. A publication authored by applicants is entitled “Friction Stir Welding as a Rivet Replacement Technology”; Brian Dracup and William Arbegast; SAE Aerofast Conference, Oct. 5, 1999.